Method of forming cathode ray tube body portion



y 5, 1964 J. c. COLEMAN ETAL 3,132,017

METHOD OF FORMING CATHODE RAY TUBE BODY PORTION Original Filed Sept. 23,1959 4 eets-Sheet 1 FIG.

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nvmvroxs d. C. Co L E MAN By RM. MAYHEW 7% 61.. CO M rmRn/EnS May 19-64J. c. COLEMAN ETAL 3,132,017

METHOD OF FORMING CATHODE RAY TUBE BODY PORTION Original Filed Sept. 23,1959 4 4 Sheets-Sheet 3 IN V EN TORS J. C. COLEMAN BY R-VV. MAYHEW hiffMay 5, 1964 Original Filed J. c. COLEMAN ETAL 3,132,017

METHOD OF FORMING CATHODE RAY TUBE BODY PORTION Sept. 25, 1959 4Sheets-Sheet 4 INVENTORS J C. dozrM/m/ By Z w. MAW/ w United StatesPatent 3,132,017 METHOD OF FORMING CATHODE RAY TUBE BODY PORTIQN JamesC. Coleman and Ray W. Mayhew, Columbus, Qhio, assignors, by mesneassignments, to Owens-Illinois Glass Company, Toledo, Ohio, acorporation of Ohio Original application Sept. 23, 1959, Ser. No.841,730. Divided and this application Apr. 4, 1960, Ser. No.

4 Claims. (Cl. 65-71) This invention relates to the manufacture ofhollow articles by centrifugal molding action and more specifically tomolding bowls or similar articles from molten glass or other molten orplastic material. The invention as herein illustrated and described isespecially adapted to the manufacture of hollow glass funnels or bodymembers for cathode-ray picture tube envelopes for television reception.

As presently manufactured, cathade-ray tube envelopes or bulbs are madeby separately fabricating a glass face plate and a hollow glass funnel.These parts are subsequently sealed together as by thermal fusion orother means. More recently, the hollow funnel has been made bycentrifugal action wherein a charge of molten glass is deposited in theapex of a hollow upwardly-facing mold and the mold is immediatelyrotated about its vertical axis to form the hollow funnel. A shorttubular portion is usually formed integral with the hollow funnel at theapex of the mold which portion is subsequently severed and replaced by alonger tubular neck member. The above steps are followed in making bothcircular and rectangular cathode-ray bulbs. Previously, the small orapex end of all commerciallyproduced funnel members has been formedhaving a circular cross-sectional configuration. This has been truewhether the screen area of the bulb has been circular or rectangular inperipheral contour. Normally a circular electrical yoke element adaptedto create an electromagnetic field to eflect proper beam deflection ismounted in close proximity to the juncture area of the funnel and itsneck tubulation. Precise control over the contour and dimensions ofglass sidewalls in this region is imperative for satisfactory clearanceand control of the cathode-ray beam which scans the tube screen. Wherethe deflected beam is surrounded by sidewalls which are circular incross-section, the raster which is scanned being rectangular in shapemust be given proper clearance to prevent the formation of shadows atcorners of the tube screen. This condition may occur when the deflectedbeam at the diagonals of its rectangular pattern is interrupted ordistorted by the sidewalls.

Concurrently with providing proper beam clearance in bulbs by preciseformation of the frusto-conical small end of the funnel, problems ofexcessive weight and undue length of the bulb as measured axiallybetween its extremities have arisen. The normally cylindrical yoke areahas recently been manufactured flaring at increasingly wider angles ofdivergence of electron beam de-. flection commensurate with practicaltube design. The industry has proceeded from beam deflection anglesincreasing from 70 to 90 and then to 110 to overcome problems ofexcessive bulb weight and overall length. The latter beam angle isutilized in so-called wide-angle bulbs.

Previously, in the manufacture of funnel parts for television picturetube envelopes, the prior art has followed the teaching of Gitfen PatentNo. 2,662,346, issued December 15, 1953, entitled Method and Apparatusfor Forming Glass. This disclosure teaches the method of introducing acharge of molten glass into an upwardly facing mold which is thenrotated to distribute centrimember in a rotatable mold.

3,132,017 Patented May 5, 1964 fugally the major portion of the glasscharge over the wall of the mold while advancing a cylindrically-shapedtool downwardly into the tubular apex portion of the mold to contact andshape the glass therein. The distributing tools as disclosed by Gilfenin the above-identified patent and in Patent No. 2,696,699, issuedDecember 14, 1954, entitled Glass Forming, all relate to shaping thevortex end of the funnel simultaneously with mold rotation to formcircular or cylindrical areas thereat having a prescribed wallthickness. Tube envelope structures fabricated in accordance with theseteachings have not provided an efficient use of beam deflection powerbecause the yoke sidewall area is circular and the raster of the beampaths in the yoke region is rectangular.

Accordingly, it is an object of the present invention to provide acathode-ray tube envelope having a structure which permits moreefficient use of electron beam deflection power.

Another object of the present invention to provide a cathode-ray tubestructure and method of fabricating its body portion which permiteffective control of electron beam deflection by improved distributionof the glass or material being molded in the deflection area and toovercome various difliculties met within conventional structures andmethods.

Another object of the present invention is toprovide a cathode-raytelevision picture tube having a funnel member which is non-circular atboth its large and small ends for improved electron beam scanning of ascreen or target area.

Another object of the invention is to provide a body member of acathode-ray tube envelope having an essentially rectangular contour atits large end and having a non-circular contour over. at least theinterior surfaces of its small end in the same orientation as the largeend.

Another object of this invention is to provide an improved method offorming a generally conical-shaped hollow glass article such as atelevision picture tube funnel by combinedly pressforming a localizedsidewall region of the article into non-circular cross-sectional contourover at least its convexly-shaped inner surfaces and centrifugallycasting the remaining extensively-flaring sidewall portions thereof.

A still further object of the present invention is to provide a methodof forming a funnel member of a cathode-ray picture tube envelope ofthermoplastic material which envelope is rectangular and geometricallysimilar at both its large and small ends by stepwise pressing its smallend into rigid form with a rectangular pattern of radially-extendingdepressions and subsequently centrifugally casting the remaining portionof said funnel The specific nature of this invention, as Well as otherobjects and advantages thereof, will become apparent to those skilled inthe art from the following detailed description taken in conjunctionwith the annexed sheets of drawings on which, by way of preferredexample only, are illustrated the preferred embodiments of thisinvention;

'On (the accompanying drawings:

FIG. 1 is a plan view of an essentially rectangular funnel member of acathode-nay tube envelope having nonoiroul-ar interior surfaces at itssmall end molded in accordarrce with the present invention.

FIG. 2 is a part-sectional elevational view of a rotatable mold andcooperative press-forming apparatus for forming such funnel member, themold being shown in initially charged arrangement.

FIG. 3 is a partial vertical sectional view showing the press-formingapparatus in cooperative arrangement with 3 the rotatable mold instationary relation during the pressing step.

FIG. 3A is a view similar to FIG. 3 showing the pressing apparatuspartially withdrawn from its molding arrangement.

FIG. 4 is a view similar to FIG. 3 showing the mold and molded articleafter rotation with the pressing apparatus fully withdrawn.

FIG. 5 is a perspective view of a cathode-ray tube showing its small endregion having a non-circular contour.

FIG. 6 is a side elevational view of such tube.

FIG. 7 is a horizontal sectional view of the tube yoke portion takenalong the line 77 of FIG. 6.

FIG. 8 is a view similar to FIG. 7 showing a modification of the tubeyoke area.

FIG. 9 is a plan view of 4a cathode-ray tube funnel member onlyfabricated in accordance with the invention.

FIG. 10 is a vertical section view of the funnel member taken along its.diagonal dimension at the line ltl-ltl of FIG. 9.

FIG. 11 is an enlarged fragmentary sectional View of the non-circularinternal surfiaces at yoke area of the funnel member taken along theline 1l-11 of FIG. 9.

As shown in FIG. 2, a mold 10, formed with a hollow body 11 and a shorttubular stem or extension 12, is mounted on a vertical rotary shalt 16for rotation ther with about its vertical axis. Shaft 13 is retained onbearings and has a pulley 14 mounted thereon which may be driven by amotor 15, and an endless belt 16 or other source of power. The lower endof the mold is closed by an ejector valve 18 vertically operable withinextension 12.

A pressing tool 20 is mounted adjacent to mold 10* for movement into andout of the mold cavity as described hereinbelow. Tool 20 is mounted on arigid shaft 21 which is in turn supported by a rock arm 22. Rock arm 22is mounted for both lateral movement in a horizontal direction andvertical reciprocating movement into and out of the mold cavity to movethe tool 20 into and out of pressing relation. Am 22 is actuated bylinkage to a reciprocating piston rod 23 which may be powered eithermechanically or pneumatically. The downward movement of arm 22 may belimited by an adjustable stop (not shown) which may be threadedlymounted on a journaled shaft. Piston 25 is reciprocatingly moved withincylinder24 to its prescribed upper and lower levels by pneumatic fluidintroduced into cylinder 24 through inlet and outlet lines 26 and 27 andpiston rod 23 is moved vertically thereby. 7

Rock arm 22 may be moved laterally by a cam follower riding in a grooveas shown in Patent No. 2,861,394 to Ruff, entitled Forming GlassArticles, issued November 25, 1958. Another form of pressing apparatusfor use in conjunction with a rotary mold is disclosed in the copendingpatent application of Clark, Serial No. 568,865, filed March 1, 1956,and entitled Machine for Centrifugal Molding of Glassware, thisapplication being assigned to the same parent assignee as the presentapplication. Both of the aforementioned disclosures relate todistributor tool mechanisms which have frusto-conical surfiaces andwhich are rotatable in conjunction with the rotarymold. This inventionhowever utilizes a stationary pressing tool which is maintained inprescribed relation devoid of angular movement during the interval ofits lowermost pressing alignment with the mold.

The lateral displacement of arm 22 away from the mold 10 permits theintroduction of a charge of molten glass into the mold. As shown in FIG.2, a gob 40 of molten glass has been deposited in mold 10 and pressingtool 20 is shown in broken lines in its extended position immediatelythereover for initiating a pressing operation.

Pressing tool 20 comprises a short cylindrical section 2011 integralwith and merging into a generally hrusto-conical section 20b generallysimilar to the shape of the apex of the funnel. The frusto-conicalsurfaces 2011 have a series of radially projecting protuberances or lugs20 4 adapted to shape the central upper surfaces of the glass chargeduring pressing with an upwardly facing peripherally-spaced rectangularpattern of radial grooves or depressions. Tool 20 has essentiallyright-cylindrical surfaces Ztld above frusto-coriical surfaces 20badapted to serve a distributing function upon an upper portion of theglass charge. Tool 20 is maintained in stationary fixed relation onshaft 21 for the pressing operation in conjunction with the mold.

The large open end of mold body 11 is generally rectangular in shapehaving a ledge portion 11a which is surrounded by an annular ring 17.Ledge 11a of the mold body and retaining ring 17 serve to restrain theuppermost portion of the glass during centrifugal spinning to form anintegral moil and prevent accidental discharge of the charge from themold duning rotation.

An upper portion of mold extension 12 has a recess 12a formed in anexternal region to facilitate the engagement of a locking device 30 toindex the mold into proper pressing orientation with pressing tool 2%.Indexing device 30 consists of an air cylindermotor 31 with an indexinglug 32 adapted to project into recess 1 lb for proper axial orientationof the mold and pressing tool. Thus, positive angular alignment betweenthe mold 10 and pressing tool 20' is obtained. Where the large open endof mold 11- is rectangular in shape in symmetry with its vertical axis,the lower region of mold may have a pair of recesses 12:: in oppositelyaligned arrangement for indexing the mold in either one of.twopositions.

According to the present method, a charge 4-0 of molten glass isdeposited in hollow mold 10 while the mold is stationary orrotating at avery slow rate (FIG. 2). A short interval of time is allotted in orderto permit the charge to settle into the apex of the mold and to indexthe mold 10 and pressing tool 20 into proper alignment. Alternately, themold may be indexed prior to being charged and before bringing thepressing tool into vertical alignment.

The, prescribed alignment consists of the diagonals at the largerectangular end of the mold being co-radial with the radially extendingprotuberances 200 on the frustoconical surfaces of the pressing tool.With the mold and pressing tool in proper alignment both axially andangularly. the tool is moved downwardly by cylinder 24 to press-form alocalized central region of the glass chargedtl into non-circular formas shown in FIG. 3. The cylindrical portion 20a of the pressing toolpenetrates the lower apex area and cylindrical portion of mold body 11and mold extension 12 in vertical alignment therewith. The mold surfacesat this area may be either cylindrical or rectangular in horizontalcross-section being indicatedas the former in the drawings. Pressingtool 20 has a properly contoured upper region 20d illustrated asessentially right-cylindrical'to distribute properly the unpressed upperportion 4% of the glass charge which remains fluid and workable for ashort interval for subsequent spinning.

immediately following the formation of the central localized portion 40bof the glass charge in the apex area of the mold, pressing tool 20 issubstantially withdrawn from contact with the glass by operation of theair cylinder motor and upward travel of piston rod 23. The glass portion4% which has been pressed thin is cooled or chilled by the combinedaction of the tool and mold to establish an initially set-up conditionwhile the upper remaining portion 4% of the charge ofgreater mass isstill at a low viscosity. After partial withdrawal of the tool 20 asshown in FIG. 3A, locking lug 32 is withdrawn from contact with the moldrecess 12a and the mold is im mediately rotated rapidly about itsvertical axis in order to distribute the remaining glass 40a along thesides of the mold by centrifugal action. The mold is rotated atsulficient angular velocity over a sufilcient interval of time to spreadand mold the remaining glass over the flaring sidewalls of the mold.Depending upon the character of the particular heat-softened materialbeing molded, retraction of the tool 20 in an upward direction afterpressing can also be controlled to leave some of the upper chargeportion 40a in contact with the upper cylindrical surfaces 20d of thetool 20 at least partially during the accelerating period of the mold toprevent the charge from slumping interiorly into the pressed region.Tool surfaces 20d can also be contoured having a non-cylindrical shapeto distribute the upper charge portion to be formed in a rectangularpattern solely by centrifugal forces.

After forming the full flaring sidewalls 40c of the article by rotation,the mold is decelerated and stopped and the molded article is cooled andhardened into final form. As shown in FIG. 4, the glass has been movedupwardly over the full sidewall surfaces of mold body 11 and over itsledge portion 11a, the glass thereabove comprising an integral moilportion of the final article which may be subsequently separated. Duringrotation, the pressformed non-circular apex area of the molded articleremains unaffected having been chilled to such a degree .by the thinningaction of the mold and tool that centrifugal force does not adverselyaffect the non-circular configuration of the glass in this region onspinning. By this prior pressing of the yoke area of the tube funnel innon-circular form, the required control of beam clearance in the finalarticle is obtained.

The excess glass from the pressing is either forced downwardly into moldextension 12 to form the tubular or nubbin portion of the article orupwardly away from the frusto-conical surfaces of the tool. The lowershort tubular portion of the article may be subsequently separatedtherefrom and a longer length of neck tubulation joined thereto insubsequent operations. As illustrated in FIGS. 1 and 5 newly-formedrectangular funnel member 40 is shown having a rectangular pattern ofradial grooves 40b formed in the same orientation as the diagonals ofits large rectangular open end.

Following formation of the funnel 40' the large open 7 end thereof maybe scored internally while the article is still retained Within the moldas the mold slowly rotates.

After this scoring operation, the ejector valve 18 in the bottom of themold is moved upwardly to separate the molded article from the moldsidewalls. The funnel is then retained in a convenient position forbeing removed from the mold. After removal of the funnel from the mold,the moil or rim portion 40d of the funnel formed above the mold ledge11a may be removed in any conventional manner as by annularly crackingit off by a differential chilling of the glass above and below the scoreline.

A completed so-called rectangulartube is shown in FIG. 5 wherein thebody part consists of a funnel 40' molded in accordance with theforegoing procedure. The large open end of the funnel has a rectangularface plate 41 sealed to its large rectangular open end and a necktubulation 42 sealed to its small end. FIG. 6 shows a completed tube ofthe wide-angle type in which the funnel 40' has been fabricated by theabove procedure. The apex area of the funnel member adjacent its necktubulation 42 has a cross-sectional shape which is cylindrical on itsexternal surfaces and has a rectangular pattern of radial recesses 40bon its inner surfaces as shown in FIG. 7. This form of yoke area permitsdeflection of the electron beam in an essentially rectangular scanningpattern for bombarding the rectangular tube screen. Thus, the deflectedbeam is provided with proper clearance as scanned in a rectangularpattern to facilitate reducing the overall length of the bulb. Also thesurrounding deflecting yoke can be brought into closer proximity to thebeam deflection point. A conventional electrical yoke element having acircular opening can be used to surround this area of the envelope forimproved utilization of beam deflection power. The depth and width ratioof recesses 4% are in no way critical so far as the tube strength isconcerned so long as the glass thickness is maintained sufficientlygreat to prevent undue strain and electrical breakthrough along withproper control of beam deflection.

A modified form of the yoke area as shown in FIG. 8 may be formedwherein the mold apex area has a modified rectangular shapegeometrically similar, or nearly so, as dictated by the configuration ofthe beam path in that region, and in the same orientation as the largeopen end of the funnel. The corner regions40e of therectangularly-shaped small end are smoothly curved in order for theenvelope to withstand the forces of atmospheric pressure loading and toprevent the development of strains thereat. Pressing tool 20 rather thanhaving radial protuberances as such as described hereinabove, has amodified rectangular shape geometrically similar to the mold apex area.Mold extension 12 also has a similar rectangular cross-sectional shape.The cooperative interaction of these parts on pressing creates a yokearea having a substantially uniform wall thickness and a preciserectangular contour which is optimum to contain the envelope of electronbeam paths. Where the external surfaces of the funnel yoke area arerectangular in shape, an electrical yoke element having a rectangularopening is utilized in conjunction'therewith.

The foregoing description sets forth a tube configuration and method offabricating its primary body portion by a completely unique procedurefor molding thermoplastic material. A tube envelope fabricated ofthermoplastic material such as glass having a neck region of rectangularor non-circular cross-section has been considered not only difficult tomanufacture as a unitary article but unattainable in large-sizecentrifugally cast workpieces. This is particularly true in forming theareas of such articles where the moment of inertia is relatively low asat the small end of a hollow funnel adjacent its axis of rotation.

The subject envelope having a non-circular contour over at least theinner surfaces of the yoke region does not produce an accumulation ofstatic charges in the corners of the neck when the surroundingelectromagnetic field is established. Further, the subject contour doesnot result in loss of electrical energy or non-linear distortions of theelectron beam.

The new cathode-ray tube envelope described above and the funnel-shapedmain body portion comprising a part of such tube envelope, as alsodescribed above, are claimed in application Serial No. 841,730, filedSeptember 23, 1959, now Patent No. 3,005,122, issued October 17, 1961,in our names, and the present application is a division of such earlierfiled application.

Various modifications of the present inventionmay be resorted to withinthe spirit and scope of the appended claims.

We claim:

1. The method of forming a generally frusto-conical shaped hollowarticle comprising the steps of introducing a heat-softened charge ofthermoplastic material into the bottom region of a hollow mold havingsidewalls flared outwardly and upwardly toward the upper end of themold, said mold having a substantially rectangular crosssection at itsupper end, pressing a portion of said charge of thermoplastic materialinto engagement with the bottom portion of the mold sidewalls, therebyforming the internal surfaces of said pressed charge portion intogenerally non-circular final configuration angularly aligned with therectangular cross-section of said mold upper end, continuing theaforesaid pressing and forming until the press-formed bottom portion ofsaid charge is substantially rigid without subjecting the molten glasstoappreciable centrifugal forces, rapidly rotating the mold about avertical axis thereby spreading and molding the remaining still-workableportion of said charge over the flaring sidewalls of said 'mold,continuing the rotation of the mold until all portions of said chargeare essentially rigid, stopping the rotation of the mold, and removingthe formed rigid charge from the mold.

2. A method in accordance with claim 1 including, after introduction ofa charge and prior to the pressing and forming of said charge, the stepsof axially aligning and rotationally orienting a pressing means with thebottom portion of said mold and, after pressing and forming said charge,the steps of maintaining said pressing means in at least partial contactwith said' charge during rotation of said mold for distribution ofthestill-workable portion of said charge.

3,. In a method of centrifugally casting-a glass article or' the like ina rotatable open-topped mold, the steps of dropping a gob of moltenglass into the mold, aligning a pressing plunger axially with the. mold,moving the plunger axially into the mold into pressing engagement with aportion of the gob, halting the plunger by the resistance of the glassgob, portion to flow between the plunger and the mold, retaining theplunger in contact with the gob for a length of time suificient toprevent" centn'fugal molding of the gob pressed portion, and rotatingthe mold to centrifugally form the non-pressed portions ofthe gob.

4., In a method of making a cathode ray tube envelope or the like havingan interior apexportion of noncircu'la'r contour by centrifugallycasting amolten glass gobin a mold rotatable about a Vertical'axis, thesteps of rotationally orienting both the mold and a pressing plunger ofnon-circular contour about said vertical axis, restraining said moldagainst rotation, inserting the pressing plunger into. the mold intocontact with the gob to press form a portion only'of the gob tothe'contour of the apex portion of the article, thereby chilling thepress formed portion of the gob intermediate the plunger and the mold toa non-flowable state while leaving the remainder of the igob flowable,retracting the, plunger from contact with the gob, releasing the moldfor rotation and subsequently rotating the mold to centrifugallydistribute the remainder of the gob Within the mold.

ReferencesCited-in the file of this patent UNITED STATES PATENTS-

1. THE METHOD OF FORMING A GENERALLY FRSTO-CONICAL SHAPED HOLLOW ARTICLECOMPRISING THE STEPS OF INTRODUCING A HEAT-SOFTENED CHARGE OFTHERMOPLASTIC MATERIAL INTO THE BOTTOM REGION OF A HOLLOW MOLD HAVINGSIDEWALLS FLARED OUTWARDLY AND UPWARDLY TOWARD THE UPPER END OF THEMOLD, SAID MOLD HAVING A SUBSTNATIALLY RECTANGULAR CROSSSECTION AT ITSUPPER END, PRESSING A PORTION OF SAID CHARGE OF THERMOPLASTIC MATERIALINTO ENGAGEMENT WITH THE BOTTOM PORTION OF THE MOLD SIDEWALLS, THEREBYFORMING THE INTERNAL SURFACES OF SAID PRESSED CHARGE PORTION INTOGENERALLY NON-CIRCULAR FINAL CONFIGURATION ANGULARLY ALIGNED WITH THERECTANGULAR CROSS-SECTION OF SAID MOLD UPPER END, CONTINUING THEAFORESAID PRESSING AND FORMING UNTIL THE PRESS-FORMED BOTTOM PORTION OFSAID CHARGE IS SUBSTANTIALLY RIGID WITHOUT SUBJECTING THE MOLTEN GLASSTO APPRECIABLE CENTRIFUGAL FORCES, RAPIDLY ROTATING THE MOLD ABOUT AVERTICAL AXIS THEREBY SPREADING AND MOLDING THE REMAINING STILL-WORKABLEPORTION OF SAID CHARGE OVER THE FLARING SIDEWALLS OF SAID MOLD,CONTINUING THE ROTATION OF THE MOLD UNTIL ALL PORTIONS OF SAID CHARGEARE ESSENTIALLY RIGID, STOPPING THE ROTATION OF THE MOLD, AND REMOVINGTHE FORMED RIGID CHARGE FROM THE MOLD.